Electric motor



Nov. 16, 1948. F. H. GERLACH ET Al.

ELECTRI C MOTOR Filed March l5, 1945' INV ENTOR /M MQ/ ATTORNEY WITNESSES Patented Nov. 16, 1948 ELECTRIC MOTOR Francis H. Gerlach, Wapakoneta, and John' D.

Miner, Jr., Lima, Ohio, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 15, 1945, Serial No. 582,854

3 Claims.

The present invention relates to small electric motors, and more particularly to amotor which is especially designed for mounting on a supporting plate with the axis of the motor at a minimum distance from the plate.

The principal object of the present invention is to provide an electric motor which can be Vmounted on a supporting plate with the axis of the motor shaft positioned at a distance from the plate which is only slightly greater than the radius of the armature of the motor. There are numerous applications of small electric motors in which it is necessary, or at least desirable, to mount the motor on a supporting member or plate in such a manner that the motor occupies as little space as possible, and in order to do this the motor shaft must be positioned as close to the supporting plate as possible. Various expedients have been used to obtain this result, but these expediente have always involved either an unsymmetrical motor construction or the use oi a single concentrated eld coil, or both. Motors of this type therefore have suffered from poor commutation, excessive magnetic leakage, excessive temperature rise due to the single concentrated coil, or a combination of these difficulties.

It is, accordingly, a, further object of the invention to provide an electric motor which can be mounted With its shaft at a minimum distance from a supporting plate, in which good commutation is obtained and the magnetic leakage flux is small, and in which the temperature rise can be kept to a reasonable value. The new motor is also capable of being rapidly and easily assembled and disassembled.

Other objects and advantages of the invention will be apparent from the following detailed' description, taken in connection with the accompanying drawing, in which:

Figure 1 is a side elevation of the new motor assembled on its supporting plate;-

Fig. 2 is a plan view of the motor without the supporting plate;

Fig. 3 is an end View of the motor, partly in section, on the line III-III of Fig. 2, and

Fig. 4 is a wiring diagram showing the electrical connections of the motor.

As previously indicated, the motor of the present invention is especially intended for applications Where the motor is of small size and must be mounted so as to occupy a minimum space. The particular motor shown in the drawing for the purpose of illustration is a universal sewing machine motor intended to be mounted on a supporting plate I which may be apart of the sewing machine structure. It is to be understood, of

course, that the construction of the present invention is oi general application and is not limited to this particular use. The motor is shown The motor itself includes a laminated core'structure 2 which is built up of a plurality of lamina--I tions secured together in a stack by means of rivets `3, or in any other suitable manner. As clearly shown in Fig. 3, the laminations'of which the core 2 is made up are generally U-shaped, having a central opening and one open side Which is adapted to abut against the supporting plate I. Polar projections 4 are formed on each of the two sides Vof the core 2 adjacent to the open side, and a field coil 5 is placed on each of the polar projections 4. The field coils 5 may be heldin place by means of metal clips 6 which extend across the outside of the core structure 2, preferably in shallow grooves so as to be flush with the surface of the core.

The core 2 is secured to the-supporting platel I by means of a metal strap or band I whichA extends aroundV the core 2, and which may be secured to the plate I in any suitable manner, as by screws 8 extending into pads 9 on the plate I. The strap I is preferably skewed, as clearly shown in the drawing, to rmly secure the core in position. It desired, the upper surface of the core 2, which abuts against the platel I, may

have grooves I0 formed in it for engagement with corresponding ribs II on the plate I in order to prevent relative displacement between the plate and the core. might be provided on the platel at the ends of the core to prevent any possibility of endwisemovement.

The rotor member or armature I2 may beof any suitable construction and is mounted on a shaft I3. A commutator I4 is also mountedon the shaft fand connected to the armature Windings, and a fan I5 may be secured to the shaft at the opposite end of the armature to force a stream of cooling air-through the motor. The shaft I3 is supported for rotation in bearingsv I6 which may be supported on the plate I, or in any other suitable manner.

Since the core structure 2 is open at the top where it 'bears against the supporting plate I, which may be of nonmagnetic material, the flux density in the polar projections 4 will not be uniform, but since the motor is symmetrical about the vertical center line, this non-uniformity in flux density has no adverse effect on the commuf It is preferred, howeverfto makethe` reluctance of the iux paththrough the polar` projections and the armature less at the-side of Y the armature adjacent to the' plate I than at the other side.

As clearly shown in Fig. 3, this variation in reluctance is accomplished by tapering theairgap f- II between the armature l2 and the polarl projections 4, so that the width of the air `gap is leastf at the side of the motor-adjacent the plate. I and If desired, similar ribs increases to its greatest width at the opposite side of the armature. This tapering oi the air gap is obtained by a slight eccentricity of the axis of the shaft I3 with respect to the polar projections or by the shape of the polar projections. With this diierence in reluctance of the ux path, a larger part of the ux is forced toward the upper side of the motor, thus tending to compensate for the incomplete magnetic circuit on that side and making the distribution ci the flux more uniform. It will be obvious that this variation in the reluctance Of the magnetic path through the polar projections and armature could also be accomplished in other ways such as by punching a hole in the lower tip of each pole to cause that portion of the pole to saturate and thus force the flux toward the upper side of the motor.

The particular motor shown. in the drawing is a universal or series motor having a governor to control the speed, the electrical connections of the motor being shown in Fig. 4, although the invention is also applicable to other types of motors. The governor lil may be of any suitable construction and has not been shown in detail, since it forms no part or the present invention. The rotating parts of the governor are mounted on the shaft I3 adjacent the commutator It, and the stationary parts of the governor, together with the brushholders i9, are mounted on. a bracket member 20 which is secured to the mounting plate I by means of screws El in position for the brushes 22, which are supported in the brushholders lil, to engage the commutator lli.

It will now be apparent that a small electric motor has been provided which can be mounted on a supporting plate with the shaft at a minimum distance from the plate which may be only slightly greater than the radius of the armature itself, and if desired, the distance might even be made equal to the radius of the armature, or slightly less, by providing a recess 23 in the plate I to give proper clearance for the rotating armature. Since the new motor is symmetrical about the vertical center line, the nonuniform flux density resulting rom the open side of the core has no adverse effect on the commutation, although this nonuniformity can be minimized by the use of a tapered air gap as described above. lThus, good commutation is readily obtained. Two separate eld coils are used, one on each of the polar projections of the core, and in this way the heat loss in the motor is distributed over a relatively large area so that the temperature rise is not excessive, and the size of the motor for a given rating can be kept small. The use of two coils in this manner also reduces the magnetic iiuX leakage so that the leakage flux is relatively small. The manner in which the motor is mounted on the supporting plate is very simple and effective, since the mating grooves i0 and ribs ll prevent relative movement between the motor and the mounting plate and the metal band l rmly holds the motor in place. The core can readily be removed, however, merely by removing one or the screws 8 and springing down the metal band l. Thus, a very desirable construction is provided for motors which must be mounted so as to occupy the smallest possible space, and the disadvantages which have resulted from previous attempts at such a motor have been substantially eliminated.

It is to be understood that although a specific embodiment of the invention has been shown and described for the purpose of illustration, the invention is not limited to the particular details of construction shown, but in its broadest aspects it includes all equivalent modifications and embodiments which come within the scope of the appended claims.

We claim as our invention:

1. An electric motor adapted to be mounted on a supporting plate positioned at a minimum distance from the axis of the motor, said motor having a generally U-shaped laminated core, the open side of the U-shaped core being adapted to abut against the supporting plate, inter-engaging means on the core and plate for preventing relative movement between. the core and plate, opposed polar projections on the core closely adjacent the open side thereof, a eld coil on each of said polar projections, a rotor member rotatably supported between the polar projections, and a longitudinally skewed strap member encircling the core for securing it to the supporting plate.

2. An electric motor adapted to be mounted on a supporting plate positioned at a minimum distance from the axis of the motor, said motor having a generally U-shaped laminated core, the open side of the U-shaped core being adapted to abut against the supporting plate, interengaging means on the core and plate for preventing relative movement between the core and plate, opposed polar projections on the core closely adjacent the open side thereof, a iield coil on each of said polar projections, a rotor member rotatably supported between the polar projections, the air gap between the rotor member and. the polar projections increasing in width from the side of the rotor member adjacent the supporting plate to the core structure having opposed salient pole portions closely adjacent the open side thereof, and the closed side of the core being closely adjacent the pole portions so that the core is of small size, a iield coil on each of said pole portions, and a rotor member rotatably supported between the pole portions with its axis spaced from the supporting plate a distance which does `not greatly exceed the radius of the rotor member, the air gap between the rotor member and the pole portions increasing in width from the side of the rotor member nearest the supporting plate to the other side of the rotor member.

FRANCIS H. GERLACH. JOHN D. MINER, Jr.

REFERENCES CITE The following references are of record in the i'ile of this patent:

Number .Name Date 516,784 Wuest MarA 20, 1894 982,78L Behrend Jan. 3l, 1911 1,205,156 Butler Nov. 21, 1916 1,216,002 Shea Feb. 13, 191'? 1,284,365 Kettering Nov. 12, 1918 2,122,374 Kohlhagen June 23, 1938 2,331,628 Piron Oct. 12, 1943 

